In drilling, it is common practice to extend the length of the drill string by adding successive individual threaded sections of drill pipe to the top of the drill string. Each additional section of pipe is threaded to the preceding section. The rotation of the drill bit at the bottom of the drill string is accomplished by rotating the entire drill string. This rotation is induced by a drilling unit at the surface or top of the drill string, which rotates a quill. The quill is threaded to the last section of pipe in the drill string. This process continues until the drill string has reached the desired depth.
Once the drilling is completed and the pipe is to be removed from the drill string, the quill is operated in the reverse direction to unthread the individual pipe sections from the drill string. However, in the absence of external forces, it is unpredictable and difficult to control which of the threaded connections in the drill string will be broken first by this reverse rotation.
To avoid this problem, a drill unit is typically used which has a mechanism to move the quill along the machine at least the length of one section of the drill pipe. To unthread a section of drill pipe, the quill is first loosely threaded to the uppermost section of drill pipe. A breakout device, which coaxially surrounds the quill, is then manually lowered to simultaneously engage both the quill and the uppermost section of drill pipe in a manner which prevents the uppermost section of drill pipe and the quill from rotating in relation to each other. This is typically accomplished by providing a breakout device having one or more channels on its internal face which engage corresponding keys on both the quill and the drill pipe. In this manner, the threaded connection between the quill and the drill pipe is prevented from separating. The quill is then retracted so that the uppermost section of drill pipe is contained within the drill unit. The end of the next lower pipe is prevented from rotating. This may be accomplished by a slip and slip bowl assembly, wrench, tong wrench or any other method of locking the drill pipe in place. The quill is then rotated in the reverse or unthreading direction to break and completely separate the threaded connection between the two uppermost sections of drill pipe in the drill string. The single uppermost section of drill pipe is then swung away from the remainder of the drill string and the quill is lowered to allow a person to manually raise the breakout device from the engaged position to the disengaged position. The quill is then rotated in the reverse or unthreading direction, while a person holds the drill pipe in place, to separate the loosely threaded connection between the quill and the drill pipe. The quill is then loosely threaded to the next uppermost section of drill pipe in the drill string and the above process repeated until the entire drill string has been retracted.
The breakout device typically has two channels that run longitudinally along opposite sides of the inside face of the breakout device. These channels allow the breakout device to simultaneously engage keys located on opposite sides of both the quill and the drill pipe when the breakout device is in the engaged position. In the disengaged position, the breakout device is moved away from the drill pipe so that the breakout device is no longer engaged with the key of the drill pipe.
The breakout device is typically held in the raised or disengaged position by a chain connected to the quill on its upper end and the breakout device on its lower end. The lower end of the chain is connected to the breakout device in a manner which allows the chain and breakout device to be disconnected from each other. Typically this is achieved by attaching a hook to the breakout device which is suited to interlock with a link in the chain. To lower the breakout device from the disengaged to the engaged position, the chain is disconnected from the hook and the breakout device is lowered over the drill pipe so that the channels of the breakout device engage the key of the drill pipe.
The hook and chain assembly used to hold the breakout device in the disengaged position presents a significant safety hazard. When the drilling unit is in operation, the hook and chain rotate with the quill and breakout device regardless of whether the breakout device is in the engaged or disengaged position. While rotating, the hook and chain may contact the drilling unit operator, or any other person, causing injury to that person. There are other disadvantages of the hook and chain assembly that will be understood by those skilled in the art.